infrastructure//cloud computing//bare metal

Bare metal is a whole physical server rented to one customer with no hypervisor between their software and the hardware, and it is how a cloud or neocloud provider offers the full performance and isolation of owning a machine while still provisioning it through an API. The customer installs the operating system directly on the hardware, sees every core, every GPU and the real network card, and shares nothing with anyone else's workload on that box. In embedded work the same words mean something different, firmware running with no operating system at all; in infrastructure they mean a server without virtualization.

Bare metal is a whole physical server rented to one customer with no hypervisor between their software and the hardware, and it is how a cloud or neocloud provider offers the full performance and isolation of owning a machine while still provisioning it through an API. The customer installs the operating system directly on the hardware, sees every core, every GPU and the real network card, and shares nothing with anyone else's workload on that box. In embedded work the same words mean something different, firmware running with no operating system at all; in infrastructure they mean a server without virtualization.

The usual cloud product is the opposite: a virtual machine carved out of a larger host by a hypervisor, which adds a small layer of overhead and shares the host's memory bandwidth, caches and devices with other tenants. For most services that cost is negligible and the flexibility (resize, migrate, replace in minutes) is worth it. For some workloads it is not:

Large GPU training wants every bit of the machine. The GPUs, the high-speed network cards for the interconnect and the local disks must be reached at full speed and with predictable timing, and a training job across a thousand GPUs runs at the pace of the slowest one, so the jitter of a shared host costs the whole cluster (training cluster).

Some software needs the hardware itself: its own hypervisor, special kernel modules, licences tied to physical cores, or strict compliance rules about sharing hardware with other customers (multi-tenancy).

Bare metal and multi-tenant are not opposites.

A provider runs one shared platform (the network, the storage, the control plane, the billing) and hands each customer dedicated physical servers inside it; the servers are single-tenant while the platform is multi-tenant. The choice is about whether the machine itself is shared, and what the customer must then manage alone.

The price of bare metal is responsibility and speed of change: the customer patches the operating system and drivers, a failed machine is replaced rather than migrated live, and provisioning takes minutes to hours rather than seconds.